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AST/ADT

Atlantic Standard Time

UTC−4

12am

3am

6am

9am

12pm

3pm

6pm

9pm

Atlantic Time is on standard time: AST (UTC−4) until Sun, Mar 14, 2027.

Keep ADT (UTC−3)

MST/MDT

Mountain Standard Time

UTC−7

3h behind

12am

3am

6am

9am

12pm

3pm

6pm

9pm

Mountain Time is on standard time: MST (UTC−7) until Sun, Mar 14, 2027.

Keep MDT (UTC−6)

Quick answers

Selected conversion

8:00 am08:00 AST (UTC-4), Nov 8, 2026 = 5:00 am05:00 MST (UTC-7), Nov 8, 2026

AST is 3 hours ahead of MST.

ADT and MDT examples

These examples always use ADT (UTC-3) and MDT (UTC-6). They stay the same when you change the date or time above. The selected conversion may differ when daylight saving time applies.

ADT is 3 hours ahead of MDT.

How the time difference changes

For most of the year, ADT is 3 hours ahead of MDT. From Nov 1, 2026 to Mar 14, 2027, and from Nov 7, 2027 to Mar 12, 2028, AST is 3 hours ahead of MST. Briefly around clock changes, ADT is 4 hours ahead of MST or AST is 2 hours ahead of MDT.

For most of the year, working hours of 9:00 am to 6:00 pm in ADT correspond to 6:00 am to 3:00 pm in MDT. At other times of the year, working hours of 9:00 am to 6:00 pm in AST correspond to 6:00 am to 3:00 pm in MST.For most of the year, working hours of 09:00 to 18:00 in ADT correspond to 06:00 to 15:00 in MDT. At other times of the year, working hours of 09:00 to 18:00 in AST correspond to 06:00 to 15:00 in MST.

Compare ADT time with MDT time, including current local time, UTC offsets, time difference, daylight saving changes, working hours, and shareable meeting times.

Time Difference

Atlantic Standard Time is 3 hours ahead of Mountain Standard Time.
8:00 am08:00 in AST is 5:00 am05:00 in MST

AST to MST call time
Best time for a conference call or a meeting is between 12pm-6pm12:00-18:00 in AST which corresponds to 9am-3pm09:00-15:00 in MST.

8:00 am08:00 Atlantic Standard Time (AST). Offset UTC -4:00 hours
5:00 am05:00 Mountain Standard Time (MST). Offset UTC -7:00 hours

8:00 am08:00 AST / 5:00 am05:00 MST

Choose an hour to update the converter. Day labels such as “next day” or “+1” are relative to the selected date in the first column. Use Up and Down arrow keys, Home or End to move between hours, then Enter or Space to select.

Hourly time comparison
AST	MST
	9:00pm previous day
	10:00pm previous day
	11:00pm previous day
	12:00am
	1:00am
	2:00am
	3:00am
	4:00am
	5:00am
	6:00am
	7:00am
	8:00am
	9:00am
	10:00am
	11:00am
	12:00pm
	1:00pm
	2:00pm
	3:00pm
	4:00pm
	5:00pm
	6:00pm
	7:00pm
	8:00pm
	21:00 previous day
	22:00 previous day
	23:00 previous day
	00:00
	01:00
	02:00
	03:00
	04:00
	05:00
	06:00
	07:00
	08:00
	09:00
	10:00
	11:00
	12:00
	13:00
	14:00
	15:00
	16:00
	17:00
	18:00
	19:00
	20:00

Atlantic Daylight Time

Offset: ADT is 3 hours behind Greenwich Mean Time (GMT).

Countries using this time zone: Bermuda, Canada, Greenland

Principal Cities: The largest city in the ADT time zone is Halifax in Canada, with about 471,559 people. Other major cities in this time zone include Sydney, Moncton, Saint John, Fredericton.

French: HAA - Heure Avancée de l'Atlantique

Map of the areas on Atlantic Daylight Time (ADT) — ADT part of the year
Today the shaded areas are on UTC−4 (Atlantic Standard Time).
Open the world time zone map © OpenStreetMap

Daylight Saving: Atlantic Daylight Time (ADT) is a daylight saving/summer time zone, but some places set clocks back one hour during winter and observe Atlantic Standard Time (AST).

End: Atlantic Daylight Time (ADT) ended on Sunday, November 1, 2026 at 2:00 am02:00 local time and clocks were set one hour back to Sunday, November 1, 2026, 1:00 am01:00 local standard time instead. Daylight saving ends annually on the first Sunday of November.

Start: Atlantic Daylight Time (ADT) starts on Sunday, March 14, 2027 at 2:00 am02:00 local time and clocks are set one hour forward to Sunday, March 14, 2027, 3:00 am03:00. Daylight saving starts annually on the second Sunday of March.

See Canada daylight saving time and upcoming clock changes worldwide.

ADT representations, usage and related time zones

W3C/ISO-8601: International standard covering representation and exchange of dates and time-related data

-03 - basic short
-0300 - basic
-03:00 - extended

Email/RFC-2822: Internet Message Format Date Standard, typically used for timestamps in email headers

-0300 - sign character (-) followed by a four digit time providing hours (03) and minutes (00) of the offset. Indicates an offset of three hours to the west of the zero meridian.

Military/NATO: Used by the U.S. military, Chinese military and others

Papa - Military abbreviation for ADT
P - short form of 'Papa'

IANA/Olson: Reflects ADT time zone boundaries defined by political bodies, primarily intended for use with computer programs and operating systems

America/Glace_Bay
America/Goose_Bay
America/Halifax
America/Moncton
America/Thule
Atlantic/Bermuda
Canada/Atlantic

Time zones with the GMT -3 offset:

ADT - Atlantic Daylight Time
PMT - Pierre & Miquelon Standard Time
PMST - Pierre & Miquelon Standard Time
AMST - Amazon Summer Time
ART - Argentina Time
BRT - Brasilia Time
CLST - Chile Summer Time
FKST - Falkland Islands Summer Time
FKT - Falkland Islands Time
GFT - French Guiana Time
P - Papa Time Zone
PYST - Paraguay Summer Time
PYT - Paraguay Time
SRT - Suriname Time
UYT - Uruguay Time

Mountain Daylight Time

Offset: MDT is 6 hours behind Greenwich Mean Time (GMT).

Countries using this time zone: Canada, Mexico, United States

Principal Cities: The largest city in the MDT time zone is Ciudad Juárez in Mexico, with about 1.512 million people. Other major cities in this time zone include Denver, El Paso, Albuquerque, Colorado Springs.

French: HAR - Heure Avancée des Rocheuses

Spanish: MT - Zona Pacífico

Map of the areas on Mountain Daylight Time (MDT) — MDT part of the year
Today the shaded areas are on UTC−7 (MST).
Open the world time zone map © OpenStreetMap

Daylight Saving: Mountain Daylight Time (MDT) is a daylight saving/summer time zone, but some places set clocks back one hour during winter and observe Mountain Standard Time (MST).

End: Mountain Daylight Time (MDT) ended on Sunday, November 1, 2026 at 2:00 am02:00 local time and clocks were set one hour back to Sunday, November 1, 2026, 1:00 am01:00 local standard time instead. Daylight saving ends annually on the first Sunday of November.

Start: Mountain Daylight Time (MDT) starts on Sunday, March 14, 2027 at 2:00 am02:00 local time and clocks are set one hour forward to Sunday, March 14, 2027, 3:00 am03:00. Daylight saving starts annually on the second Sunday of March.

See USA daylight saving time and upcoming clock changes worldwide.

MDT representations, usage and related time zones